Cal. CIV § 945.5

A builder, general contractor, subcontractor, material supplier, individual product manufacturer, or design professional, under the principles of comparative fault pertaining to affirmative defenses, may be excused, in whole or in part, from any obligation, damage, loss, or liability if the builder, general contractor, subcontractor, material supplier, individual product manufacturer, or design professional, can demonstrate any of the following affirmative defenses in response to a claimed violation:

(a) To the extent it is caused by an unforeseen act of nature which caused the structure not to meet the standard. For purposes of this section an “unforeseen act of nature” means a weather condition, earthquake, or manmade event such as war, terrorism, or vandalism, in excess of the design criteria expressed by the applicable building codes, regulations, and ordinances in effect at the time of original construction.

(b) To the extent it is caused by a homeowner’s unreasonable failure to minimize or prevent those damages in a timely manner, including the failure of the homeowner to allow reasonable and timely access for inspections and repairs under this title. This includes the failure to give timely notice to the builder after discovery of a violation, but does not include damages due to the untimely or inadequate response of a builder to the homeowner’s claim.

(c) To the extent it is caused by the homeowner or his or her agent, employee, general contractor, subcontractor, independent contractor, or consultant by virtue of their failure to follow the builder’s or manufacturer’s recommendations, or commonly accepted homeowner maintenance obligations. In order to rely upon this defense as it relates to a builder’s recommended maintenance schedule, the builder shall show that the homeowner had written notice of these schedules and recommendations and that the recommendations and schedules were reasonable at the time they were issued.

(d) To the extent it is caused by the homeowner or his or her agent’s or an independent third party’s alterations, ordinary wear and tear, misuse, abuse, or neglect, or by the structure’s use for something other than its intended purpose.

(e) To the extent that the time period for filing actions bars the claimed violation.

(f) As to a particular violation for which the builder has obtained a valid release.

(g) To the extent that the builder’s repair was successful in correcting the particular violation of the applicable standard.

(h) As to any causes of action to which this statute does not apply, all applicable affirmative defenses are preserved.